TITLE: GCN CIRCULAR NUMBER: 44760 SUBJECT: GRB 260601A: Fermi GBM Observation DATE: 26/06/01 18:13:56 GMT FROM: A. Holzmann Airasca at University of Trento and INFN Bari <a.holzmannairasca@unitn.it> A. Holzmann Airasca (UniTrento and INFN Bari) reports on behalf of the Fermi Gamma-ray Burst Monitor Team: "At 11:00:12.44 UT on 01 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260601A (trigger 802004417/260601458). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 15.06, Dec = 44.38 (J2000 degrees, equivalent to J2000 1h 0m, +44d 22'), with a statistical uncertainty of 2.03 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a mixture of two Gaussians, one with a radius of 1.8 degrees (52% contribution) and one with a radius of 4.1 degrees (47% contribution) [A. Goldstein et al. 2020, ApJ, 895, 1]). The angle from the Fermi LAT boresight is 30 degrees. The GBM light curve consists of a single emission episode with a duration (T90) of about 0.8 s (50-300 keV). The time-averaged spectrum from T0-0.07 to T0+0.34 s is best fit by a power law function with an exponential high-energy cutoff. The power law index is -0.63 +/- 0.02 and the cutoff energy, parameterized as Epeak, is 960 +/- 30 keV. The event fluence (10-1000 keV) in this time interval is (2.08 +/- 0.06)E-06 erg/cm^2. The 64-ms peak photon flux measured starting from T0+0.064 s in the 10-1000 keV band is 40 +/- 1 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 750 +/- 20 keV, alpha = -0.57 +/- 0.05 and beta = -2.0 +/- 0.2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/" View this GCN Circular online at https://gcn.nasa.gov/circulars/44760. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...